1. Field of the Invention
The present invention relates to an optical device used in an optical pickup for recording and/or reproducing information against optical information recording media, such as optical discs.
2. Description of the Related Arts
In the optical discs as information recording media, conventionally, there are known CD (Compact Disc), DVD (Digital Versatile Disc), BD” (Blu-ray Disc) for high density recording and so on. These optical discs are being required with large capacity and high density. With such requirements, it is contemplated that the optical pickup for reproducing and/or recording information from and to these optical discs is provided with a light source of short-wavelength and an improved numerical aperture of an objective lens. In addition, light receiving/emitting elements and optical components constituting an optical pickup are also required to have dimensions and mutual positional relationships of high accuracy.
With a wide variety of applications of optical discs, a recording/reproducing device is also required with improved portability and therefore, the optical pickup is required to satisfy not only high reliability but miniaturization and weight saving. Coping with these requirements, there is provided an optical device that includes, as constituents, a semiconductor laser (or laser unit) forming a light source of the optical pickup, a PDIC (Photo Detector IC) forming a substrate for a light receiving element, a hologram element having optical-path converting and optical-path dividing functions and also lens function and a mirror, all of which are collected to one body for integration. Also in this optical device, with the provision of an optical disc with large capacity and high density, respective components forming the optical pickup are also required to have dimensions and mutual positional relationships of high accuracy and also price-reduction.
In Japanese Patent Publication Laid-open No. 2005-056480, there is proposed an optical device where an optical-path conversion mirror, a sub-mount and a semiconductor laser are mounted in separated components on a PDIC, while the semiconductor laser is united with a light receiving element for integration.
In addition, in Japanese Patent Publication Laid-open No. 2000-196176, there is disclosed an optical device where a light receiving element substrate, an optical-path conversion mirror and a sub-mount are united with each other, while a semiconductor laser is mounted on a PDIC through the intermediary of no sub-mount.